por Rhinoceros beetle It is the common name given to the species that are part of the Dynastinae subfamily. The insects that make up this group are characterized by their large size and their physical appearance, where the large horns stand out.
These beetles are distributed throughout the world, except in the polar areas. As for their habitat, they prefer humid tropical forests and mature forests.
In such ecosystems, the rhinoceros beetle lives among the decaying stems and leaves, on which it feeds. In addition, the adult usually eats fruits, leaves and roots.
In relation to its reproduction, it is sexual. The unicorn beetle, as it is also known, undergoes a complete metamorphosis. Thus, it goes through the stages of egg, larva, pupa to finally become an adult, capable of mating.
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Characteristics of the rhinoceros beetle
Body
The body of the adult rhinoceros beetle is covered by a thick exoskeleton. In addition, it has a pair of thick wings, known as elytra. Below these, it has other wings, of a membranous type. These allow the beetle to fly, although it does not do so efficiently due to its large size.
The tarsal claws are nearly all the same size. The exception to this feature is present in the males of some Pentodontini. In these, the protarsal claws are markedly enlarged.
Size
The size of the species that make up the Dynastinae subfamily is very varied. However, in general they can grow up to 18 centimeters. Thus, one of the smallest is the American rhinoceros beetle (Xyloryctes jamaicensis), which measures between 25 and 28 millimeters long.
The largest in the clade is the hercules beetle (dynastes hercules), which has a total length of 18 cm, of which approximately 10 cm correspond to the horn.
Coloration
Due to the great diversity of species, the range of colors of the rhinoceros beetle is very wide. Some may have brilliant coloration, with iridescent and metallic tones. Others are black, green, gray or dark brown. In addition, its body may be covered in hair, thus giving it a velvety appearance.
On the other hand, in certain insects, such as the hercules beetle, the color of the male varies, depending on the humidity level of the surrounding environment.
Thus, in the event that the atmosphere is dry, the elytra have a yellow or olive green tone. These turn black when the humidity rises considerably. The mechanism associated with these tonality changes is related to the internal structure of the elytra.
Head
In the rhinoceros beetle, the upper lip, or labrum, is hidden beneath a shield-like structure known as the clypeus. Regarding the antennae, they have between 9 or 10 segments. Usually the last three form a single structure.
Regarding the dentition, the presence varies among the members of the subfamily. For example, members of the Cyclocephalini tribe do not possess mouthparts on the lateral edge of their mandibles. Contrarily, the species of the Phileurini tribe have teeth.
horns
The rhinoceros beetle’s horns project as rigid cuticular growths. These are born from the prothorax and/or from the head. Regarding its development, it occurs from the epidermal tissue of the larvae, which later proliferates, forming a disc.
The three-dimensional shape of the adult horn originates from a structure of several dermal folds. These unfold as the beetle passes from the larval stage to the pupa.
The size and shape of the male’s horn is variable. Thus, the rhinoceros beetle has two horns, one thoracic and one cephalic, which resemble pincers.
Another striking species is the elephant beetle. This has a large central horn on its head, the end of which is divided in two. On the sides of the thorax, two shorter conical horns project.
The growth of this structure is affected by various factors, including food. According to various investigations carried out, the development of the horns is highly influenced by the physiological and nutritional state of the animal.
Experts point out that these structures are used during contests between males, for the option to mate with the female. The intent of these aggressive interactions is not to injure the opponent, but to force him out of the box.
The evolution of the horn
The Scarabaeidae family consists of approximately 35,000 species. Of these, the vast majority do not have horns. However, some complete families have such structures. In this sense, specialists propose a hypothesis that supports the presence of horns in these clades.
The approach suggests that horns existed before beetles diversified. Thus, the experts maintain that there are indications that suggest the presence of this structure in the ancestors of this insect.
One of these is that the vast majority of hornless subfamilies have at least one species with rudimentary horns, as is the case with the families Pleocomidae and Ochodaeidae.
Also, some beetles in the pupal stage develop structures similar to thoracic horns. This would be an indication that the adult ancestors probably had these antlers.
If this hypothesis is true, it means that the lack of horns in most current beetles is a condition that implies the suppression of the growth of said structure.
State of conservation
Some of the rhinoceros beetle populations are threatened with extinction. Such is the case of calicnemis latreilleiwhich has been categorized by the IUCN as a species at risk of disappearing from its natural habitat.
This beetle lives in Algeria, France, Italy and Spain. In these regions, the environment is degraded, due to the felling and deforestation of forests. In addition, forest lands are used to build urban elements and tourist structures.
Regarding conservation actions, several of the areas where the calicnemis latreillei They are under the protection of national and international organizations.
On the other hand, some species, such as the hercules beetle (dynastes hercules), lack sufficient data to know its conservation status.
However, the rain forests where they live are fragmented and degraded, due to the action of climate change and deforestation. In addition, a large number of species of the Dynastinae subfamily are captured, to be sold internationally as pets.
These factors affect the communities of this insect, and may have a negative impact on its development.
Habitat and distribution
Rhinoceros beetles are widespread on all continents, with the exception of the polar regions and Antarctica. Although its distribution is very wide, the highest population density is found in the tropics.
Geographic location of some species
Rhinoceros beetles, which live in the United States, are found southward from northeastern Arizona to the state of Nebraska.
Numerous populations inhabit Central America. For example, in Panama and Costa Rica there are around 157 species, many of which have been recently described. Such is the case of Cyclocephala amazon, C.labidion, C. mustache and c stockwelli.
In Guatemala and Honduras is found the Mayan dynasties. Likewise, the cornizuelo (Megasoma Elephas) lives from southern Mexico to northern Venezuela and Colombia.
In relation to South America, it extends widely throughout all the tropical regions of the continent. Thus, the enema bread lives in the Cerrado-Pantanal ecotone (Mato Grosso, Brazil).
Another South American species is the Acteon beetle (Megasoma acteon), found in Bolivia, Colombia, Brazil, Ecuador, Guyana. Peru, Panama, Venezuela and Suriname.
Some of these beetles have a much more extensive distribution, such as the European rhinoceros beetle (Oryctes nasicornis). It lives in Europe up to the central region of the Scandinavian Peninsula, North Africa, Western and Central Asia.
In contrast, the canary rhinoceros beetle (oryctes prolixus) is found only in the western islands of the Canary archipelago.
Habitat
Due to its extensive range, habitats are highly diverse. Among these are humid forests, tropical forests, laurel forests, oak forests and lowlands.
In such ecosystems, the rhinoceros beetle lives in the decaying wood of shrubs and trees. Also, it can be found between the roots or between the stems of palm leaves.
Fallen logs and leaf litter provide the insect with a safe hiding place. In this, it can take shelter during the day, to protect itself from the threats of its predators.
For some species, like the Megasoma elephasthe lowland forested areas are a suitable environment for its development.
However, they prefer mature forests. The reason for this is that these ecosystems have a large number of plant species, which are absent in the youngest forests.
In addition, in mature forested areas there are large numbers of dead logs on the ground and standing, which are in various states of decomposition.
These constitute an ideal environment for the nesting and growth of the larvae, which feed exclusively on this plant material.
Taxonomy and subspecies
taxonomy
-Animal Kingdom.
-Subkingdom: Bilateria.
-Infrakingdom: Protostomy.
-Superphylum: Ecdysozoa.
-Filum: Arthropoda.
-Subphylum: Hexapoda.
-Class: Insecta.
-Subclass: Pterygota.
-Infraclass: Neoptera.
-Superorder: Holometabola
-Order: Coleoptera.
-Superfamily: Scarabaeoide.
-Family: Scarabaeidae.
-Subfamily: Dynastinae.
tribes
Agaocephalini
Members of this tribe have horns or tubercles on their heads and pronotums. In addition, they have a wide jaw, which may or may not have teeth. The elytra present an irregular dotting.
Regarding its distribution, it is found in the tropical regions of the New World, where there are 11 genera and approximately 40 species.
Cyclocephalini
This tribe is made up of 13 genera, which are restricted to the New World, with the exception of the monobasic genus Ruteloryctes, which is in Africa.
The legs of this beetle have cylindrical tarsi, while in almost all species the anterior tarsi are enlarged. Regarding the jaws, they lack teeth.
dynastini
This tribe is made up of three genera, which inhabit the New World. The members of this clade are within the group of the largest insects on Earth.
Males generally have horns on their heads and pronotums. As for the females, the vast majority lack a horn, but they may have tubercles on their heads.
Oryctini
The males of this tribe…